A typo sent firefighters racing to a wrong address, leaving six people trapped and injured in their burning Brooklyn building, sources said.

It was the second delayed response incident on the same day, including one fire in which two little boys and their dad died.

Sources said a caller reached 911 Wednesday around 9:06 a.m., telling a female operator a fire was raging at 570 Lefferts Ave. in Crown Heights. The operator mistakenly entered 470 Lefferts. She faces possible discipline. Six people were hurt, none seriously.

Hours later, two people called in the wrong address for a fire at 654 St. Marks Ave., where two boys and their father died. Unions also said a new way 911 calls are handled played a role in that delayed response.